Tell girl X that she's telling girl Y that you're all going out that night. Bar hop. Don't stay in one place for too long. You should hit at least three different places before the night is over. Bring them both back to your place.
When you're there, get them comfortable and in your room. Tell them about a friend [whoever] of yours who is a guru and a shaman and teaches classes on dual-induction massage. He talked you into being a Guinea pig for his two students, and it was the most incredible experience of your life. Explain that dual-induction massage is when two people massage one person in perfect synchronization. The mind cant process all of the movements, so it disconnects from reality and instead feels like a thousand hands are massaging you.
MAKE SURE YOU DESCRIBE IT WITH ENTHUSIASM. And don't give them a chance to say no.
Tell girl Y to get on her stomach - you will want to start with the girl who is most nervous/shy/jealous about the situation. Given that girl X has already told you that she wants it, viola, you don't even have to guess which girl to start with.
Tell girl Y to follow your movements exactly.
After a while, tell them to massage you. Take your shirt off. The building sexual energy will weigh on them very soon if it hasn't already, and it will draw them to you - and to each other.
When it's girl X's turn, make sure she takes her shirt off. See if you can get girl Y to do it for her (and for you

). Tell girl Y to follow your every move, too, and make this massage more erotic. Start massaging her back, then move down to her calves, work up her thighs (especially inner thighs), butt, up the back, sides of her breasts. Position you and girl Y so that you are facing one another. Draw her in and kiss her. Lightly moan during the kiss - audible stimulation will turn her and girl Y on.
Turn girl X over, and both you and girl Y should start making out with her. Make it a game. Tell girl Y that you both should keep doing the same thing. Kiss both sides of girl X's neck, nibble her ears, then work down and suck her tits. Take her pants/etc. off and go down on her together. After a while, pull girl X up and turn your attentions completely onto girl Y. After similar SPAM, it will be your turn and they will want to double team you.
Bring your A-game bro.